This invention relates to a bore hole rock shear tester and method for using same.
In many mining and excavating operations, it is desirable to test the shear strength of rock being excavated or mined. Sometimes this is done by taking samples of the rock to the laboratory. However, such laboratory tests are often costly and biased. A more cost effective and unbiased manner of testing is to bore a hole in the rock in its natural environment.
In situ shear strength testing of the rock is accomplished by boring a hole and by inserting test equipment into the hole. The test equipment is used to engage an envelope of material on the wall of the bore hole. Then, radial and axial forces are exerted on the envelope of material until shearing occurs.
Previous devices for accomplishing this rock bore hole shear test are cumbersome and difficult to use. These devices require a large diameter test bore hole. This required large diameter of the test bore hole causes the tests in rock to be very expensive. If it were possible to use a smaller diameter bore hole, these tests would be easier to conduct and less expensive.
Previous bore hole testing devices required independent apparatus for exerting normal and axial forces on the walls of the bore hole. The equipment for normal stress application included hydraulic cylinders which were embodied in the device and which were inserted into the hole with the device. Because this equipment was required to be inserted into the bore hole, there was a necessity for a rather large diameter bore hole in order to conduct the test.
Prior devices for conducting the rock bore hole shear test were cumbersome to use. It was necessary to remove these devices from the hole several times during the test so that they could be cleaned and checked to assure proper readings.
Therefore, a primary object of the present invention is an improved rock bore hole shear testing device and method for using same.
A further object of the present invention is the provision of a testing device which permits the application of normal and axial forces to the wall of the bore hole with apparatus which is located externally of the bore hole.
A further object of the present invention is the provision of a device which could operate within a hole which is one and one-half inches in diameter, the diameter commonly used in mining, for roof bolting and blasting.
A further object of the present invention is the provision of a device and method for using same, which would require only one insertion of the testing device into the bore hole.
A further object of the present invention is the provision of a device which can be applicable to both shallow and deep testing holes.
A further object of the present invention is the provision of a device which is simple in construction and operation so that it can be used by a mining crew involved in regular drilling processes.
A further object of the present invention is the provision of a device which permits first, the application of a normal force to seat the testing apparatus firmly in the walls of the bore hole, and second, to permit the simultaneous application of both a normal and an axial force to the bore hole wall so as to determine the point at which the device causes shearing in the walls of the bore hole.
A further object of the present invention is the provision of a device which is economical to manufacture, durable in use and efficient in operation.